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Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn4+-activated deep red phosphor GdGeSbO6:x%Mn4+ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn4+ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO6:0.3%Mn4+ produces a narrow emission peak centred at 682 nm in the range of 650–800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited 2Eg → 4A2g transition of Mn4+ ions. Notably, the optimal phosphor GdGeSbO6:0.3%Mn4+ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance (I423 K/I303 K ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO6:0.3%Mn4+ phosphors with commercial phosphors on the surface of a 365 nm UV chip. [ABSTRACT FROM AUTHOR]

Te4+-doped Cs2ZrCl6 vacancy-ordered perovskites with excitation wavelength-dependent tunable color have been synthesised by a simple precipitation method at room temperature, with two luminescent centres originating from the Te4+ and the STE (self-trapping exciton) of the Cs2ZrCl6 itself, respectively. They exhibit two different emission characteristics at 254 nm and 365 nm excitation wavelengths. At an excitation wavelength of 254 nm, the emission characteristics allow Te4+-doped Cs2ZrCl6 to exhibit tunable emission from blue to white to yellow under the control of Te4+ doping. And the excitation wavelength of 365 nm shows yellow emission. Te4+ doped Cs2ZrCl6 phosphors were used for optical anti-counterfeiting, and the anti-counterfeiting patterns were well distinguished under 254 nm and 365 nm UV lamps, demonstrating the potential of this excitation wavelength-dependent tunable color material for optical anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

At present, tuning the luminescence characteristics of phosphors by external physical stimuli such as temperature and pressure has attracted the interest of researchers. However, the emission-tunable luminescence processes by temperature or pressure in lead-free perovskite with ordered vacancy materials have not been systematically studied. In this study, Bi3+-doped Rb2SnCl6 crystals were successfully synthesized using a simple precipitation method, and these crystals demonstrated a remarkable enhancement of luminescence intensity compared with the unannealed ones at 140–200 °C, and with a red-shift in the emission peak from 450 to 500 nm. It was found that the annealing treatment increased the Bi–Cl bond length leading to emission red-shift and achieved the change in the emission intensity due to the band gap modulation of the material. Furthermore, a candidate material for the color-changing optical security strategies was obtained by combining the Bi3+-doped Rb2SnCl6 phosphor and printing ink. This work is a valuable reference for the rational design of luminescent perovskites with promising new functionalities and stimulates the great potential of luminescent perovskites in developing promising phosphors for advanced anticounterfeiting. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu3+/DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu3+/DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu3+/DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu2+ and Cr2O72− in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu2+ and Cr2O72− in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu2+ and Cr2O72−. [ABSTRACT FROM AUTHOR]

The optical properties of Mn4+-activated phosphors are heavily affected by the host and the related data are difficult to obtain, which makes quantitative design of novel phosphors with required wavelength particularly challenging. In the era of big data, computation is emerging as a vital complement to materials development. Compared with traditional calculation routes, machine learning (ML) models provide better solutions for the problems wherein understanding the underlying physics is complicated with sparse data. In this study, we developed six ML models based on a sparse and small data set to rapidly predict the peak emission wavelength of novel phosphors and use Recursive Feature Elimination (RFE) to select the best features. Among them, the K-nearest neighbors regression (KNN.r) algorithm using non-parametric regression technology can predict the value of the target variable based on the similarity between the target value and its spatial neighbors, which can tackle sparse data sets with no obvious linear relationship well and has the best prediction accuracy. These models were then used to predict 278 potential Mn4+-activated phosphor hosts extracted from the inorganic crystal structure database (ICSD), and 19 samples were selected to validate these methods. In order to overcome the lack of physical and chemical insight of KNN, a visual data analysis was carried out based on hierarchical clustering analysis (HCA), and the rule between the peak emission wavelength and the structure of host was proposed. Guided by the results of KNN and HCA, six samples were selected for the synthesis and characterization to verify our conclusions. The measured values of all these phosphors exhibit good agreement with the predicted results, suggesting the success of our methodology. Thus, the model established and the rule proposed in this paper provide a new pathway for the rapid discovery of novel phosphors. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu3+/DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu3+/DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu3+/DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu2+ and Cr2O72− in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu2+ and Cr2O72− in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu2+ and Cr2O72−. [ABSTRACT FROM AUTHOR]

Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn 4+ -activated deep red phosphor GdGeSbO 6 : x %Mn 4+ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn 4+ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO 6 :0.3%Mn 4+ produces a narrow emission peak centred at 682 nm in the range of 650-800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited 2 E g → 4 A 2g transition of Mn 4+ ions. Notably, the optimal phosphor GdGeSbO 6 :0.3%Mn 4+ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance ( I 423 K / I 303 K ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO 6 :0.3%Mn 4+ phosphors with commercial phosphors on the surface of a 365 nm UV chip.

At present, tuning the luminescence characteristics of phosphors by external physical stimuli such as temperature and pressure has attracted the interest of researchers. However, the emission-tunable luminescence processes by temperature or pressure in lead-free perovskite with ordered vacancy materials have not been systematically studied. In this study, Bi 3+ -doped Rb 2 SnCl 6 crystals were successfully synthesized using a simple precipitation method, and these crystals demonstrated a remarkable enhancement of luminescence intensity compared with the unannealed ones at 140-200 °C, and with a red-shift in the emission peak from 450 to 500 nm. It was found that the annealing treatment increased the Bi-Cl bond length leading to emission red-shift and achieved the change in the emission intensity due to the band gap modulation of the material. Furthermore, a candidate material for the color-changing optical security strategies was obtained by combining the Bi 3+ -doped Rb 2 SnCl 6 phosphor and printing ink. This work is a valuable reference for the rational design of luminescent perovskites with promising new functionalities and stimulates the great potential of luminescent perovskites in developing promising phosphors for advanced anticounterfeiting.

Metal-organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu 3+ /DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu 3+ /DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu 3+ /DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu 2+ and Cr 2 O 7 2- in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu 2+ and Cr 2 O 7 2- in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu 2+ and Cr 2 O 7 2- .

Single-matrix white light-emitting diodes are still a challenge. Achieving tunable white light emission from lead-free perovskites attracts much attention. Herein, nanoscale Rb 2 SnCl 6 (RSC) vacancy ordered double perovskite were synthesized by an optimized precipitation method. Further, using ns 2 ions (Bi 3+ , Te 4+ , and Sb 3+ ) doped RSC vacancy ordered double perovskite to obtain broadband blue, yellow-green, and orange-red emission. The color temperature adjustable high-quality white light emission based on the codoping strategy is obtained by controlling the doping ratio of Bi 3+ and Te 4+ . Additionally, the white light-emitting diodes encapsulated by this single matrix white luminescent material exhibit excellent stability. Combined with theoretical calculations, it is elucidated that these high-efficiency emissions are not only derived from the unique electronic transition of ns 2 ions but also related to the energy band properties and the crystal field. This work shows that ns 2 ions doped RSC vacancy ordered double perovskite can meet the needs of different luminous colors and color temperature tunable white light emission. Meanwhile, it is a strong competitor to replace the lead-based perovskite.